NAME¶

std::ranges::views::adjacent,std::ranges::adjacent_view,std::ranges::views::pairwise - std::ranges::views::adjacent,std::ranges::adjacent_view,std::ranges::views::pairwise

Synopsis¶

Defined in header <ranges>
template< ranges::forward_range V, std::size_t N >

requires ranges::view<V> && (N > 0) (1) (since C++23)
class adjacent_view

: public ranges::view_interface<adjacent_view<V, N>>
namespace views {

template< std::size_t N >
inline constexpr /* unspecified */ adjacent = /* unspecified (2) (since C++23)
*/ ;

}
namespace views {

inline constexpr auto pairwise = adjacent<2>; (3) (since C++23)

}
Call signature
template< ranges::viewable_range R >

requires /* see below */ (since C++23)

constexpr ranges::view auto adjacent<N>( R&& r );

1) adjacent_view is a range adaptor that takes a view, and produces a view whose
i^th element (a "window") is a std::tuple that holds N references to the elements of
the original view, from i^th up to i + N - 1^th inclusively.
Let S be the size of the original view. Then the size of produced view is:
* S - N + 1, if S >= N,
* 0 otherwise, and the resulting view is empty.
2) The name views::adjacent<N> denotes a RangeAdaptorObject. Given a subexpression e
and a constant expression N, the expression views::adjacent<N>(e) is
expression-equivalent to
* ((void)e, auto(views::empty<tuple<>>)) if N is equal to 0,
* adjacent_view<views::all_t<decltype((e))>, N>(e) otherwise.
3) The name views::pairwise denotes a RangeAdaptorObject that behaves exactly as
views::adjacent<2>.

adjacent_view always models forward_range, and models bidirectional_range,
random_access_range, or sized_range if adapted view type models the corresponding
concept.

Member functions¶

constructor constructs a adjacent_view
(C++23) (public member function)
begin returns an iterator to the beginning
(C++23) (public member function)
end returns an iterator or a sentinel to the end
(C++23) (public member function)
size returns the number of elements. Provided only if the underlying
(C++23) (adapted) range satisfies sized_range.
(public member function)
Inherited from std::ranges::view_interface
empty returns whether the derived view is empty. Provided if it satisfies
(C++20) sized_range or forward_range.
(public member function of std::ranges::view_interface<D>)
cbegin returns a constant iterator to the beginning of the range.
(C++23) (public member function of std::ranges::view_interface<D>)
cend returns a sentinel for the constant iterator of the range.
(C++23) (public member function of std::ranges::view_interface<D>)
operator bool returns whether the derived view is not empty. Provided if
(C++20) ranges::empty is applicable to it.
(public member function of std::ranges::view_interface<D>)
front returns the first element in the derived view. Provided if it
(C++20) satisfies forward_range.
(public member function of std::ranges::view_interface<D>)
back returns the last element in the derived view. Provided if it satisfies
(C++20) bidirectional_range and common_range.
(public member function of std::ranges::view_interface<D>)
operator[] returns the n^th element in the derived view. Provided if it satisfies
(C++20) random_access_range.
(public member function of std::ranges::view_interface<D>)

Deduction guides

(none)

Nested classes

iterator the iterator type
(C++23) (exposition-only member class template*)
sentinel the sentinel type used when adjacent_view is not a common_range
(C++23) (exposition-only member class template*)

Helper templates

template< class V, size_t N >

inline constexpr bool ranges::enable_borrowed_range<adjacent_view<V, (since C++23)
N>> =

ranges::enable_borrowed_range<V>;

This specialization of ranges::enable_borrowed_range makes adjacent_view satisfy
borrowed_range when the underlying view satisfies it.

Notes¶

There are similarities between ranges::adjacent_view and ranges::slide_view:

* Both create a "sliding window" of size N.
* Both have the same size S - N + 1, where S is the size of an adapted view such
that S >= N > 0.

The differences between these adapters are:

View adaptor value_type The window size N
ranges::adjacent_view A std::tuple object A template parameter
ranges::slide_view A range A runtime parameter

Feature-test macro Value Std Feature
std::ranges::zip_view,
__cpp_lib_ranges_zip 202110L (C++23) std::ranges::zip_transform_view,
std::ranges::adjacent_view,
std::ranges::adjacent_transform_view

Example¶

// Run this code

#include <array>
#include <format>
#include <iostream>
#include <ranges>
#include <tuple>

int main()
{
constexpr std::array v{1, 2, 3, 4, 5, 6};
std::cout << "v = [1 2 3 4 5 6]\n";

for (int i{}; std::tuple t : v | std::views::adjacent<3>)
{
auto [t0, t1, t2] = t;
std::cout << std::format("e = {:<{}}[{} {} {}]\n", "", 2 * i++, t0, t1, t2);
}
}

Output:¶

v = [1 2 3 4 5 6]
e = [1 2 3]
e = [2 3 4]
e = [3 4 5]
e = [4 5 6]

References¶

* C++23 standard (ISO/IEC 14882:2023):

* 26.7.25 Adjacent view [range.adjacent]

See also¶

ranges::adjacent_transform_view a view consisting of tuples of results of
views::adjacent_transform application of a transformation function to adjacent
(C++23) elements of the adapted view
(class template) (range adaptor object)
ranges::slide_view a view whose M^th element is a view over the M^th
views::slide through (M + N - 1)^th elements of another view
(C++23) (class template) (range adaptor object)
ranges::chunk_view a range of views that are N-sized non-overlapping
views::chunk successive chunks of the elements of another view
(C++23) (class template) (range adaptor object)
ranges::stride_view a view consisting of elements of another view,
views::stride advancing over N elements at a time
(C++23) (class template) (range adaptor object)